<em># 声明焦点事件</em>
<em>FocusNode</em> <s>focusNode</s> = <em>new</em> <q>FocusNode( )</q>;
<em># 监听焦点事件</em>
<u>@override</u>
<em>void</em> <u>initState( )</u> {
	super.<u>initState()</i>;
	<s>focusNode</s>.<b>addListener</b>(( ){
		<em>print(focusNode.hasFocus.toString( ));</em>
	});
}
<em># 使用</em>
<u>C</u>(
	<i>focusNode</i> : <s>focusNode</s>
)